Method of manufacturing photo masks

ABSTRACT

In a method of manufacturing a photo mask for lithography, circuit pattern data are acquired. A pattern density, which is a total pattern area per predetermined area, is calculated from the circuit pattern data. Dummy pattern data for areas having pattern density less than a threshold density are generated. Mask drawing data is generated from the circuit pattern data and the dummy pattern data. By using an electron beam from an electron beam lithography apparatus, patterns are drawn according to the mask drawing data on a resist layer formed on a mask blank substrate. The drawn resist layer is developed using a developing solution. Dummy patterns included in the dummy pattern data are not printed as a photo mask pattern when the resist layer is exposed with the electron beam and is developed.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.17/080,652 filed Oct. 26, 2020, now U.S. Pat. No. 11,327,405, which is adivisional application of U.S. patent application Ser. No. 15/966,862filed Apr. 30, 2018, now U.S. Pat. No. 10,816,892, which claim priorityto U.S. Provisional Application No. 62/586,085 filed on Nov. 14, 2017,the entire contents of each of which are incorporated herein byreference.

TECHNICAL FIELD

The disclosure relates to methods of manufacturing photo masks used in asemiconductor manufacturing process.

BACKGROUND

As semiconductor device feature sizes have decreased to sizes smallerthan the wavelength of light used in photolithographic processes, thediffraction of light at feature pattern edges formed on the reticlecauses a loss of resolution in transferring the reticle pattern to thewafer photoresist. Although patternable minimum resolution (e.g.,pattern pitch) is limited by an optical lithography tool (e.g., opticalscanner/stepper), design rule for a semiconductor device requiressmaller or finer pattern resolution. At the same time, requirements forphoto masks become tighter and tighter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1A shows various stages of a sequential mask making processrelating to embodiments of the present disclosure;

FIG. 1B shows various stages of a sequential mask making processrelating to embodiments of the present disclosure;

FIG. 1C shows various stages of a sequential mask making processrelating to embodiments of the present disclosure;

FIG. 1D shows various stages of a sequential mask making processrelating to embodiments of the present disclosure.

FIG. 2A shows an energy distribution of the scattered electron beamswith a total energy distribution. FIG. 2B shows a simulation result ofthe traveling path of the backscattering electrons. FIG. 2C shows a maskpattern indicating line-and-space patterns. FIG. 2D shows energydistributions of the forward scattering. FIG. 2E shows energydistributions of the backward scattering, caused by electron beamirradiations. FIG. 2F shows an overall energy distribution andcorresponding CD variation.

FIG. 3 shows a flowchart illustrating a method of manufacturing photomasks for a semiconductor manufacturing operation according to anembodiment of the present disclosure.

FIG. 4A shows a mask pattern without non-printable dummy patterns, andFIG. 4B shows a mask pattern with non-printable dummy patterns accordingto an embodiment of the present disclosure.

FIG. 5A shows a mask pattern without non-printable dummy patterns, andFIG. 5B shows a mask pattern with non-printable dummy patterns accordingto another embodiment of the present disclosure.

FIG. 6A shows non-printable dummy patterns according to an embodiment ofthe present disclosure, and FIG. 6B shows non-printable dummy patternsaccording to another embodiment of the present disclosure.

FIG. 7A shows a process for determining areas for non-printable dummypatterns according to an embodiment of the present disclosure;

FIG. 7B shows a process for determining areas for non-printable dummypatterns according to an embodiment of the present disclosure.

FIG. 8A shows non-printable dummy patterns according to an embodiment ofthe present disclosure, and FIG. 8B shows non-printable dummy patternsaccording to another embodiment of the present disclosure.

FIG. 8C shows another embodiment of generating photo mask data withnon-printable dummy patterns;

FIG. 8D shows another embodiment of generating photo mask data withnon-printable dummy patterns;

FIG. 8E shows another embodiment of generating photo mask data withnon-printable dummy patterns;

FIG. 8F shows another embodiment of generating photo mask data withnon-printable dummy patterns;

FIG. 8G shows another embodiment of generating photo mask data withnon-printable dummy patterns.

FIG. 8H shows another embodiment of generating photo mask data withnon-printable dummy patterns.

FIG. 9A shows a photo mask data generating apparatus according to anembodiment of the present disclosure;

FIG. 9B shows a photo mask data generating apparatus according to anembodiment of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The device may be otherwise oriented (rotated 90 degrees orat other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“made of” may mean either “comprising” or “consisting of.” In thepresent disclosure, a phrase “one of A, B and C” means “A, B and/or C”(A, B, C, A and B, A and C, B and C, or A, B and C), and does not meanone element from A, one element from B and one element from C, unlessotherwise described.

Embodiments of the present disclosure provide a method of manufacturinga photo mask used in a manufacturing operation of a semiconductor deviceand an apparatus for generating photo mask data for fabricating photomasks.

Many photo masks (also called reticles) are used for lithographyoperations in a semiconductor manufacturing process. The photo masks aregenerally formed using an electron beam lithography process. FIGS. 1A-1Dshow a general method of manufacturing a photo mask relating toembodiments of the present disclosure. It is understood that in thesequential manufacturing process, one or more additional operations canbe provided before, during, and after the stages shown in FIGS. 1A-1D,and some of the operations described below can be replaced or eliminatedfor additional embodiments of the method. The order of theoperations/processes may be interchangeable.

As shown in FIG. 1A, a mask blank having a transparent mask substrate100 and a pattern layer 110 formed thereon is provided, and a photoresist layer 120 is formed on the pattern layer 110. The transparentmask substrate 100 is made of, for example, a synthetic quartz having ahigh transparency for ultra violet light and deep ultra violet light(e.g., 245 nm light emitted from a KrF excimer laser or 193 nm lightemitted from an ArF excimer laser). The photo resist layer 120 issensitive to an energy beam, such as an electron beam, and either apositive photo resist or a negative photo resist. The pattern layer 110is an opaque layer made of Cr or a Cr based material in someembodiments. In other embodiments, the pattern layer 110 is asemi-transparent layer made of a Mo based material for a phase shiftmask. The pattern layer 110 is a single layer or a multilayer structure.

According to mask pattern data, the mask blank with the photo resistlayer 120 is exposed with an electron beam 150 in an electron beamlithography tool, as shown in FIG. 1B. The electron beam drawings areperformed by scanning the electron beam and moving a mask stage on whichthe mask blank is placed. After the exposure by the electron beam, theexposed photo resist layer 120 is developed with a developing solutionand a photo resist pattern 122 is formed as show in FIG. 1C. Then, byusing the photo resist pattern 122 as an etching mask, the pattern layer110 is etched by dry and/or wet etching and a mask pattern 112 is formedon the mask substrate 100, as shown in FIG. 1D.

In the electron beam lithography, the electron beam is irradiated to aplace corresponding to a desired pattern. For example, when forming ahole pattern, the electron beam is irradiated to an area of a positivephoto resist corresponding to the hole pattern, and when forming a linepattern, the electron beam is irradiated to an area of a negative photoresist corresponding to the line pattern. A positive photo resist or anegative photo resist is selected in view of the density of patterns tobe irradiated such that the total areas of the irradiated regions aresmaller than the total areas of the non-irradiated regions.

FIGS. 2A-2F show an impact of critical dimension (CD) uniformity causedby an electron beam proximity effect. An electron beam used in a photomask fabrication process generally has a small beam area (a spot beam).When an electron beam is applied to an object (e.g., a photo resist),there is a forward scattering 201 and a backward scattering 202 as shownin FIG. 2A, which shows an energy distribution of the scattered electronbeams with a total energy distribution 203. FIG. 2B shows a simulationresult of the traveling path of the backscattering electrons. As shownin FIG. 2A, the scattered electrons have a broad tail portions, whichmay overlap an adjacent pattern irradiated.

FIG. 2C shows a mask pattern indicating line-and-space patterns. Thepeaks correspond to electron beam irradiated portions for lines. FIG. 2Dshows energy distributions of the forward scattering, and FIG. 2E showsenergy distributions of the backward scattering, caused by electron beamirradiations. FIG. 2F shows an overall energy distribution andcorresponding CD variation. As shown in FIG. 2F, the line widths of theleft and right end patterns are smaller than the remaining patterns,which is called electron beam proximity effect. As shown in FIG. 2F, theleft and right end patterns receive less electron scattering effectsthan other patterns. If a single and isolated pattern is formed, thereis substantially no electron scattering effect. In other words, the CDvariation caused by the electron beam proximity effect is affected bythe surrounding pattern situation, in particular, a pattern density.

Further, when a photo resist layer, which is generally formed by anorganic material, is irradiated with electron beams, electrons areaccumulated in the irradiated portions of the photo resist. Theaccumulated electrons cause an undesired electron field, affecting theorbit of an incoming electron beam, which is called an electricalcharging effect. Similar to the electron beam proximity effect, theelectrical charging effect depends on a pattern density.

According to one aspect of the present disclosure, one or more dummypatterns are provided to suppress the undesired electron beam proximityeffect and electrical charging effect. In particular, the dummy patternsare not printable as a photo resist pattern. In some embodiments, asize, a density and/or a dose amount for the dummy patterns are adjustedsuch that the irradiated portions of the photo resist do not form adistinctive resist pattern. In certain embodiments, size, a densityand/or a dose amount for the dummy patterns are adjusted such that atotal dose amount per predetermined area for the dummy patterns issubstantially equal to a total dose amount per predetermined area foractual patterns. In other embodiments, size, a density and/or a doseamount for the dummy patterns are adjusted such that a total dose amountper predetermined area for the actual patterns and the dummy patterns iswithin a predetermined range.

FIG. 3 shows a flowchart illustrating a method of manufacturing photomasks for a semiconductor manufacturing operation according to anembodiment of the present disclosure. It is understood that in thesequential manufacturing process, one or more additional operations canbe provided before, during, and after the stages shown in FIG. 3 andsome of the operations described below can be replaced or eliminated foradditional embodiments of the method. The order of theoperations/processes may be interchangeable.

At step S301 of FIG. 3, a circuit pattern layout for one layer in asemiconductor device is designed by using a mask design tool (e.g., anelectronic design automation (EDA) tool). The circuit pattern layout forone layer is for one photo mask. In some embodiments, a multiplepattering method is utilized and in such a case, the circuit patternlayout for one layer is divided into multiple photo masks. The circuitpattern layout is generally expressed by polygon data in, for example,GDS-II stream format or in Open Artwork System Interchange Standardformat.

At step S302, circuit pattern layout data created by the mask designtool is acquired by a photo mask data generating apparatus. The photomask data generating apparatus is a separate computer system than themask design tool in some embodiments, and is a part of the mask designtool in other embodiments.

Then at step S303, a pattern density of the circuit pattern layout datais calculated. The pattern density is defined a ratio per predeterminedarea (e.g., a unit area) of patterns to be irradiated with an electronbeam with respect to the predetermined area. After calculating thepattern density, one or more areas having a pattern density equal to orlower than a threshold pattern density are identified, at step S304. Insome embodiments, the threshold density is in a range from about 20% toabout 40% (e.g., 30%). For example, a memory cell pattern generally hasa higher pattern density, while a peripheral I/O pattern generally has alow pattern density. When the pattern density of a given area is equalto or lower than the threshold pattern density, the given area isidentified as a low pattern density area, while an area of which patterndensity given area is higher than the threshold pattern density isidentified as a high pattern density (dense) area. In other embodiments,when the pattern density of a given area is lower than the thresholdpattern density, the given area is identified as a low pattern densityarea, while an area of which pattern density given area is equal to orhigher than the threshold pattern density is identified as a highpattern density area.

At step S305, dummy patterns are generated for the low pattern densityareas identified at step S304. In some embodiments, the dummy patternsare fine patterns smaller than the resolution limit of an electron beamlithography tool used to fabricate the photo masks. The pattern size ina pattern layout generally refers to an actual circuit pattern sizeformed on a semiconductor wafer. Thus, when the photo mask is a 4× mask,the pattern size on a photo mask is four times a pattern size on thesemiconductor wafer. In the present disclosure, the pattern size of thedummy patterns and circuit patterns are that on a photo mask, unlessotherwise indicated. Thus, for example, the resolution limit of theelectron beam lithography tool is 40 nm, i.e., the actual size on thephoto mask is 40 nm, the dummy patterns on the pattern layout data havea size less than 160 nm for a 4× mask, or less than 200 nm for a 5×mask. The resolution limit is also affected by a performance of a photoresist and/or a subsequent etching operation. Thus, the size of thedummy patterns is decided considering an overall mask fabricatingprocess capability, and id a practical resolution limit of the maskmaking process. In some embodiments, after the dummy patterns aregenerated, the process returns to step S303.

Then, as step S306, the original circuit pattern layout data and thedummy pattern data are combined to generate mask drawing data for theelectron beam lithography tool. In some embodiments, the electron beamlithography tool requires its own data format, and in such case, aformat conversion operation is performed on the mask drawing data.

At step S307, according to the mask drawing data, a photo resist layerformed on a mask blank is exposed with an electron beam, similar to theoperations explained with respect to FIGS. 1A and 1B. Then, the exposedphoto resist layer is developed with a developing solution at step S308,similar to the operations explained with respect to FIG. 1C. As stepS309, by using the developed photo resist pattern as an etching mask, apattern layer is etched by dry and/or wet etching and a mask pattern isformed on the mask substrate, similar to the operations explained withrespect to FIG. 1D. Then, mask inspection and mask repair operations areperformed.

In the foregoing embodiments, the dummy patterns are smaller than thepractical resolution limit of the mask making process. Accordingly,after the etching of the pattern layer, there is no patterncorresponding to the dummy pattern. In the case where a positive photoresist is used, an area of the photo resist corresponding to the dummypattern is irradiated with an electron beam. Although the irradiatedarea may be partially removed by the developing process, the photoresist remains and thus the underlying pattern layer is not etched.

In other embodiments, the dummy patterns have a size larger than thepractical resolution limit of the mask making process using the electronbeam lithography tool. In such a case, when the dummy patterns are drawnon the photo resist by an electron beam, a dose amount of the electronbeam for the dummy patterns is set smaller than a dose amount for theactual circuit patterns to be printed. In some embodiments, the doseamount of the electron beam for the dummy patterns is set smaller than athreshold dose amount, which is less than a dose amount by which thephoto resist layer forms a pattern in the development operation. Whenthe dose amount of the dummy patterns are different (smaller) than theactual circuit patterns, such information is attached to the dummypatterns (e.g., a flag) and send to an electron beam lithography tool.

FIG. 4A shows a mask pattern without non-printable dummy patterns, andFIG. 4B shows a mask pattern with non-printable dummy patterns accordingto an embodiment of the present disclosure. Methods, materials,configurations, dimensions and/or processes the same as or similar tothe foregoing embodiments may be employed in the following embodiments,and detailed explanation thereof may be omitted.

As set forth above, by analyzing the original circuit pattern layout,one or more high pattern density areas 410 are identified within a photomask layout 400, as shown in FIG. 4A. By identifying the high patterndensity areas 410, the remaining areas are identified as low patterndensity areas 420.

In some embodiments, the pattern density of the high pattern densityareas 201 is, for example, from 30% or more, which means that thethreshold pattern density is set 30%. Then, as shown in FIG. 4B,non-printable dummy patterns 430 are generated to fill the low patterndensity areas. The non-printable dummy patterns are dummy patterns ofwhich the size is smaller than the resolution limit of the electron beamlithography tool or the practical resolution limit of the mask makingprocess and/or dummy patterns to be exposed at lower exposure doseamounts that do not cause distinctive photo resist patterns.

In some embodiments, the pattern density of the non-printable dummypatterns 430 is set to the same amount as the threshold pattern density.In some embodiments, the non-printable dummy patterns are generated suchthat a pattern density of the non-printable dummy patterns is in a rangefrom 0.8 times the threshold density to 1.2 times the threshold densityof the high pattern density areas.

In other embodiments, the average pattern density of the high densityareas are calculated, and the non-printable dummy patterns 430 aregenerated to have a pattern density the same as the average patterndensity. In certain embodiments, the non-printable dummy patterns aregenerated such that a pattern density of the non-printable dummypatterns is in a range from 0.8 times the threshold density to 1.2 timesthe average pattern density of the high pattern density areas.

In the embodiment of FIG. 4B, all of the low pattern density areas arefilled with non-printable dummy patterns. In other embodiments, only apart of the low pattern density areas are filled with non-printabledummy patterns.

FIG. 5A shows a mask pattern without non-printable dummy patterns, andFIG. 5B shows a mask pattern with non-printable dummy patterns accordingto another embodiment of the present disclosure. Methods, materials,configurations, dimensions and/or processes the same as or similar tothe foregoing embodiments may be employed in the following embodiments,and detailed explanation thereof may be omitted.

Similar to FIG. 4A, by analyzing the original circuit pattern layout,one or more high pattern density areas 510 and 515 are identified withina photo mask layout 500, as shown in FIG. 5A. By identifying the highpattern density areas 510 and 515, the remaining areas are identified aslow pattern density areas 520. Then, as shown in FIG. 5B, non-printabledummy patterns 530 and 535 are generated for the areas surrounding thehigh pattern density areas 510 and 515.

In this embodiment, as shown in FIG. 5B, the non-printable dummypatterns are generated for the areas within a predetermined distancefrom the give a high pattern density area. For example, thenon-printable dummy pattern area 530 surrounds the high pattern densityarea 510 within a predetermined distance W1. In some embodiments, thepredetermined distance W1 is in a range from 100 μm to 5000 μm on aphoto mask, and in other embodiments, the predetermined distance is in arange from 500 μm to 2000 μm on a photo mask.

In some embodiments, the pattern density of the non-printable dummypatterns 530 or 535 is set to the same amount as the threshold patterndensity. In some embodiments, the non-printable dummy patterns 530 or535 are generated such that a pattern density of the non-printable dummypatterns 530 or 535 is in a range from 0.8 times the threshold densityto 1.2 times the threshold density of the high pattern density areas 510or 515.

In other embodiments, the average pattern density of the high densityareas 510 or 515 are calculated, and the non-printable dummy patterns530 or 535 are generated to have a pattern density the same as theaverage pattern density of the high pattern density areas 510 or 515,respectively. In certain embodiments, the non-printable dummy patterns530 or 535 are generated such that a pattern density of thenon-printable dummy patterns 530 or 535 is in a range from 0.8 times thethreshold density to 1.2 times the average pattern density of the highpattern density areas 510 or 515, respectively.

FIG. 6A shows non-printable dummy patterns according to an embodiment ofthe present disclosure, and FIG. 6B shows non-printable dummy patternsaccording to another embodiment of the present disclosure. Methods,materials, configurations, dimensions and/or processes the same as orsimilar to the foregoing embodiments may be employed in the followingembodiments, and detailed explanation thereof may be omitted.

In some embodiments, the non-printable dummy patterns have a squareshape having a size smaller than the resolution limit and areperiodically arranged in a matrix, as shown in FIG. 6A. In someembodiments, the non-printable dummy patterns 615 have a length L1 andL2 and are arranged with a pitch P1 and P2, respectively. In certainembodiments, L1=L2 and P1=P2, and in such a case, the pattern density ofthe non-printable dummy patterns 615 can be defined as (L1/P1)². Byadjusting the pitch P1 or P2, the pattern density of the non-printabledummy patterns 615 can be adjusted. As shown in FIG. 6A, thenon-printable dummy patterns 615 are generated to have a distance D1from the actual circuit patterns 610. The distance D1 is in a range fromabout 500 nm to 5000 nm on a photo mask.

In FIG. 6B, line-and-space patterns periodically arranged in onedirection are used as non-printable dummy patterns 625. Theline-and-space patterns have a width (length) L3 and a pitch P3, whichis smaller than the resolution limit as shown in FIG. 6B. The patterndensity of the non-printable dummy patterns 625 can be defined as(L3/P3). By adjusting the pitch P3, the pattern density of thenon-printable dummy patterns 615 can be adjusted. As shown in FIG. 6B,the non-printable dummy patterns 625 are generated to have a distance D2from the actual circuit patterns 620. The distance D2 is in a range fromabout 500 nm to 5000 nm on a photo mask.

FIGS. 7A and 7B show a process for determining areas for non-printabledummy patterns according to an embodiment of the present disclosure.Methods, materials, configurations, dimensions and/or processes the sameas or similar to the foregoing embodiments may be employed in thefollowing embodiments, and detailed explanation thereof may be omitted.

As shown in FIG. 7A, the photo mask area 700 is divided into a pluralityof sub areas 710 arranged in a matrix. The size of each of the pluralityof sub areas 710 is in a range from 50 μm to 2500 μm on a photo mask,and in other embodiments, the size is in a range from 100 μm to 1000 μmon a photo mask. In some embodiments, each of the plurality of sub areas710 has a square shape.

Within each of the plurality of sub areas 710, a pattern density iscalculated, and then sub areas having a pattern density higher than athreshold pattern density are identified as a high pattern density area(or sub areas having a pattern density lower than a threshold patterndensity are identified as a low pattern density area). In an embodiment,as shown in FIG. 7B, high pattern density areas 720, 730, 740, 750 and760 are identified.

Then, as shown in FIG. 7B, dummy pattern areas 725, 735, 745, 755 and765, in which non-printable dummy patterns generated to adjust thepattern density of the dummy pattern areas, are provided to surround thehigh pattern density areas 720, 730, 740, 750 and 760, respectively. Insome embodiments, the pattern density of each dummy pattern area afterthe non-printable dummy patterns are generated in the dummy pattern areais equal to a predetermined pattern density. In certain embodiments, thepredetermined pattern density is the same as the threshold patterndensity that is used to define the high pattern density areas and thelow pattern density areas. In other embodiments, the pattern density ofeach dummy pattern area after the non-printable dummy patterns aregenerated in the dummy pattern area is about 0.8 times to about 1.2times the average pattern density of the corresponding high patterndensity area. For example, the pattern density of dummy pattern area 725after the non-printable dummy patterns are generated is about 0.8 timesto about 1.2 times the average pattern density of the high patterndensity area 720. In certain embodiments, the pattern density of eachdummy pattern area after the non-printable dummy patterns are generatedin the dummy pattern area is equal to the average pattern density of thecorresponding high pattern density area.

FIG. 8A shows non-printable dummy patterns according to an embodiment ofthe present disclosure, and FIG. 8B shows non-printable dummy patternsaccording to another embodiment of the present disclosure. Methods,materials, configurations, dimensions and/or processes the same as orsimilar to the foregoing embodiments may be employed in the followingembodiments, and detailed explanation thereof may be omitted.

In the following embodiments, two or more threshold pattern densitiesare sets. For example, low pattern density areas 820 having a lowerpattern density than a first threshold pattern density, middle patterndensity areas 860 and 870 having a pattern density higher than the firstthreshold pattern density and lower than a second threshold patterndensity (higher than the first threshold pattern density), and highpattern density areas 810 and 815 having a pattern density higher thanthe second threshold pattern density are identified within a photo mask800, as shown in FIG. 8A.

In the embodiments of FIGS. 5A and 5B or 7A and 7B above, when thepattern density of a given area is more than (or, equal to or more than)the threshold pattern density, the area is identified as a high patterndensity area and an adjacent area having a smaller pattern density thanthe threshold is identified as a low pattern density area. However, insome cases, the pattern density of the low pattern density area adjacentto the high pattern density area is close to the threshold. For example,the threshold pattern density is 30% and the pattern density of the lowpattern density area adjacent to the high pattern density area is 29%.In such a case, it may not be necessary to provide non-printable dummypatterns to adjust the pattern density because adding non-printabledummy patterns increases mask data processing time and the amount of themask data.

In the embodiments of FIGS. 8A and 8B, the non-printable dummy patternsare provided when the high pattern density area is adjacent to the lowpattern density area and no non-printable dummy pattern is providedaround the middle pattern density areas and high pattern density areaadjacent to the middle pattern density area. In FIG. 8B, dummy patternarea 835 is provided only around the high pattern density area 815 andno non-printable dummy pattern area is provided around high patterndensity area 810 and the middle pattern density area 860 and 870. Insome embodiments, a different in percent points between the firstthreshold and the second threshold is in a range from about 5 to 20(e.g., 30% vs 25-10%). In other embodiments, two or more middle patterndensity areas are identified. In the embodiments of FIGS. 8A and 8B,when the pattern density drastically changes (high pattern density areato low pattern density area) in adjacent sub areas, non-printable dummypatterns are provided to surround the higher pattern density sub area.In certain embodiments, when the pattern density of sub areas changes5-20 percentage points (e.g., 30% vs 25-10%), non-printable dummypatterns are provided. In some embodiments, the pattern density afterthe non-printable dummy patterns are provided is the same as the patterndensity of the average of the middle pattern density areas.

Further, after the non-printable dummy patterns are provided, thepattern density of the entire photo mask is re-calculated. Then, it isdetermined whether there are adjacent sub areas having abrupt densitychange (e.g., 5-20 percentage points). When the adjacent sub areashaving abrupt density change are found, additional non-printable dummypatterns are provided.

FIGS. 8C-8G show another embodiment of generating photo mask data withnon-printable dummy patterns. Methods, materials, configurations,dimensions and/or processes the same as or similar to the foregoingembodiments may be employed in the following embodiments, and detailedexplanation thereof may be omitted.

FIG. 8C shows actual circuit patterns with a high density area (left)and a low density area (right). FIG. 8D shows non-printable dummypatterns provided in the entire area of the circuit patterns of FIG. 8C.Then, the actual circuit patterns of FIG. 8C are enlarged (biased) by,for example, about 500 nm to 5000 nm on a photo mask (same as D1 or D2of FIGS. 6A and 6B). The biased amount (D1, D2) may be adjusteddepending on the pattern density and/or mask fabrication process. Next,a logical operation is performed between the mask data of FIG. 8D andFIG. 8E by subtracting the data of FIG. 8E from the data of FIG. 8D.FIG. 8F is the result of the subtraction. Then, a logical operation isperformed between the mask data of FIG. 8F and FIG. 8C by adding thedata of FIG. 8C and the data of FIG. 8F. FIG. 8G is the result of theaddition, which shows photo mask data with actual circuit patterns andnon-printable dummy patterns.

FIG. 8H shows another embodiment of generating photo mask data withnon-printable dummy patterns. Methods, materials, configurations,dimensions and/or processes the same as or similar to the foregoingembodiments may be employed in the following embodiments, and detailedexplanation thereof may be omitted.

In this embodiments, the mask area is divided into small areas (grids),for example, about 100 μm×100 μm to about 1000 μm×1000 μm (e.g., 256μm×256 μm), and the pattern density of the layout patterns arecalculated for each small area. The small areas are not necessarily asquare. In FIG. 8H, the patterns are divided into five pattern densityareas, each of which has patterns within a predetermined pattern densityrange. For example, PD1 is for areas having a pattern density of10%-20%, PD2 is areas having a pattern density of 20%-30%, PD3 is forareas having a pattern density of 30%-40%, PD4 is for areas having apattern density of more than 40%, and PD5 is for areas having a patterndensity of less than 10%. The ranges of the pattern density are merelyan example and other ranges can be utilized. Then, non-printable dummypatterns are provided around each area to make the pattern density ofthe entire mask uniform (e.g., a variation (max-min) of patterndensities is less than 10%). In some embodiments, the operationsexplained with respect to the foregoing embodiments (e.g., FIGS. 8C-8Gor others) are performed on each area.

FIGS. 9A and 9B show a photo mask data generating apparatus according toan embodiment of the present disclosure. FIG. 9A is a schematic view ofa computer system that executes the photo mask data generating processaccording to one or more embodiments as described above. All of or apart of the process, method and/or operations of the foregoingembodiments can be realized using computer hardware and computerprograms executed thereon. In FIG. 9A, a computer system 900 is providedwith a computer 901 including an optical disk read only memory (e.g.,CD-ROM or DVD-ROM) drive 905 and a magnetic disk drive 906, a keyboard902, a mouse 903, and a monitor 904.

FIG. 9B is a diagram showing an internal configuration of the computersystem 900. In FIG. 9B, the computer 901 is provided with, in additionto the optical disk drive 905 and the magnetic disk drive 906, one ormore processors 911, such as a micro processing unit (MPU), a ROM 912 inwhich a program such as a boot up program is stored, a random accessmemory (RAM) 913 that is connected to the MPU 911 and in which a commandof an application program is temporarily stored and a temporary storagearea is provided, a hard disk 914 in which an application program, asystem program, and data are stored, and a bus 915 that connects the MPU911, the ROM 912, and the like. Note that the computer 901 may include anetwork card (not shown) for providing a connection to a LAN.

The program for causing the computer system 900 to execute the functionsof the photo mask data generating apparatus in the foregoing embodimentsmay be stored in an optical disk 921 or a magnetic disk 922, which areinserted into the optical disk drive 905 or the magnetic disk drive 906,and transmitted to the hard disk 914. Alternatively, the program may betransmitted via a network (not shown) to the computer 901 and stored inthe hard disk 914. At the time of execution, the program is loaded intothe RAM 913. The program may be loaded from the optical disk 921 or themagnetic disk 922, or directly from a network.

The program does not necessarily have to include, for example, anoperating system (OS) or a third party program to cause the computer 901to execute the functions of the photo mask data generating apparatus inthe foregoing embodiments. The program may only include a commandportion to call an appropriate function (module) in a controlled modeand obtain desired results.

In the programs, the functions realized by the programs do not includefunctions that can be realized only by hardware in some embodiments. Forexample, functions that can be realized only by hardware, such as anetwork interface, in an acquiring unit that acquires information or anoutput unit that outputs information are not included in the functionsrealized by the above-described programs in some embodiments.Furthermore, a computer that executes the programs may be a singlecomputer or may be multiple computers.

Further, the entirety of or a part of the programs to realize thefunctions of the photo mask data generating apparatus is a part ofanother program used for photo mask fabrication processes in someembodiments. In addition, the entirety of or a part of the programs torealize the functions of the photo mask data generating apparatus isrealized by a ROM made of, for example, a semiconductor device in someembodiments.

As set forth above, by identifying high pattern density areas in photomask data and adding non-printable dummy patterns, it is possible toreduce the electron beam proximity effect and/or the electrical chargingeffect in electron beam lithography for fabricating a photo mask. Insome embodiments, by limiting areas for the non-printable dummypatterns, it is possible to suppress an increase in data volume of thephoto mask data. Further, by using regularly arranged dummy patterns, itis possible to suppress an increase in data volume of the photo maskdata.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

In accordance with an aspect of the present disclosure, in a method ofmanufacturing a photo mask for lithography, circuit pattern data areacquired. A pattern density, which is a total pattern area perpredetermined area, is calculated from the circuit pattern data. Dummypattern data for areas having pattern density less than a thresholddensity are generated. Mask drawing data is generated from the circuitpattern data and the dummy pattern data. By using an electron beam froman electron beam lithography apparatus, patterns are drawn according tothe mask drawing data on a resist layer formed on a mask blanksubstrate. The drawn resist layer is developed using a developingsolution. Dummy patterns included in the dummy pattern data are notprinted as a photo mask pattern when the resist layer is exposed withthe electron beam and is developed. In one or more of the foregoing orfollowing embodiments, a dose amount of the electron beam for the dummypatterns included in the dummy patterns data is smaller than a doseamount of the electron beam for circuit patterns included in the circuitpatterns data. In one or more of the foregoing or following embodiments,the dose amount of the electron beam for patterns corresponding to thedummy patterns data is set smaller than a threshold dose amount, and thethreshold dose amount is less than a dose amount by which the resistlayer forms a pattern by the developing using the developing solution.In one or more of the foregoing or following embodiments, a size of thedummy patterns is less than a resolution limit of a patterning operationusing the electron beam lithography apparatus. In one or more of theforegoing or following embodiments, the dummy pattern data includesperiodically arranged dummy patterns. In one or more of the foregoing orfollowing embodiments, the dummy pattern data is generated such that apattern density of the areas after the dummy patterns are provided is ina range from 0.8 times the threshold density to 1.2 times the thresholddensity. In one or more of the foregoing or following embodiments, thedummy pattern data is generated such that a pattern density of the areasafter the dummy patterns are provided is equal to the threshold density.In one or more of the foregoing or following embodiments, the thresholddensity is in a range from 20% to 40%. In one or more of the foregoingor following embodiments, the dummy pattern data is generated such thatthe dummy patterns are arranged to surround a dense area having apattern density equal to or greater than the threshold density, within apredetermined distance from the dense area. In one or more of theforegoing or following embodiments, the predetermined distance is in arange from 100 μm to 5000 μm. In one or more of the foregoing orfollowing embodiments, the dummy pattern data is generated such that apattern density of an entirety photo mask after the dummy patterns areprovided is within a predetermined range. In one or more of theforegoing or following embodiments, the predetermined range is a rangefrom 0.8 times the threshold density to 1.2 times the threshold density.In one or more of the foregoing or following embodiments, thepredetermined range is more than 0.5 times the threshold density andless than the threshold density. In one or more of the foregoing orfollowing embodiments, a first threshold density and a second thresholddensity different from the first threshold density are set as thethreshold density. The dummy pattern data is generated such that firstdummy patterns are arranged to surround a first area having a patterndensity equal to or greater than the first threshold density, and seconddummy patterns are arranged to surround a second area having a patterndensity equal to or greater than the second threshold density. A patterndensity of first dummy patterns is different from a pattern density ofsecond dummy patterns.

In accordance with another aspect of the present disclosure, a photomask data generating apparatus includes a processor and a non-transitorycomputer readable medium storing a program. The program, when executedby the processor, causes the mask data generating apparatus to perform:acquiring circuit pattern data, calculating pattern density from thecircuit pattern data, generating dummy pattern data for areas havingpattern density less than a threshold density, generating mask drawingdata by combining the circuit pattern data and the dummy pattern data,and outputting the generated mask drawing data to an electron beamlithography apparatus. Dummy pattern data includes dummy patterns notprintable as a photo mask pattern when a resist layer formed on a maskblank substrate is exposed with an electron beam by an electron beamlithography apparatus and is developed. In one or more of the foregoingor following embodiments, the dummy pattern data is generated such thata pattern density of the areas is in a range from 0.8 times thethreshold density to 1.2 times the threshold density. In one or more ofthe foregoing or following embodiments, the dummy pattern data includesperiodically arranged dummy patterns. In one or more of the foregoing orfollowing embodiments, the threshold density is in a range from 20% to40%. In one or more of the foregoing or following embodiments, the dummypattern data is generated such that the dummy patterns are arranged tosurround a dense area having a pattern density equal to or greater thanthe threshold density, within a predetermined distance from the densearea. In one or more of the foregoing or following embodiments, thepredetermined distance is in a range from 100 μm to 5000 μm on a photomask.

In accordance with another aspect of the present disclosure, anon-transitory computer readable medium stores a program. The program,when executed by a processor in a mask data generating apparatus, causesthe mask data generating apparatus to perform: acquiring circuit patterndata, calculating pattern density from the circuit pattern data,generating dummy pattern data for areas having pattern density less thana threshold density, generating mask drawing data by combining thecircuit pattern data and the dummy pattern data, and outputting thegenerated mask drawing data to an electron beam lithography apparatus.The size of dummy patterns included in the dummy pattern data is smallerthan a resolution limit of a patterning operation using the electronbeam lithography apparatus.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A pattern formation method, comprising: acquiringcircuit pattern data; generating base dummy pattern data for an entirecircuit area; enlarging each pattern of the circuit pattern data togenerate enlarged circuit pattern data; logically combining the enlargedcircuit data pattern and the base dummy pattern data to generate dummypattern data; and generating drawing data by combining the dummy patterndata and the circuit pattern data, wherein dummy patterns included inthe dummy pattern data not printable as a pattern when a resist layerformed on a substrate is exposed with an electron beam by an electronbeam lithography apparatus and is developed.
 2. The pattern formationmethod of claim 1, wherein a logical operation of the logicallycombining the enlarged circuit data pattern and the base dummy patterndata comprises logical subtraction.
 3. The pattern formation method ofclaim 1, wherein a size of the dummy patterns is less than a resolutionlimit of a patterning operation using the electron beam lithographyapparatus.
 4. The pattern formation method of claim 1, wherein the dummypattern data includes periodically arranged dummy patterns.
 5. Thepattern formation method of claim 1, wherein each pattern of the circuitpattern data is enlarged by 500 nm to 5000 nm.
 6. The pattern formationmethod of claim 1, further comprising: drawing, by using the electronbeam from an electron beam lithography apparatus, patterns according tothe drawing data on the resist layer formed on the substrate; anddeveloping the drawn resist layer using a developing solution.
 7. Apattern formation method, comprising: acquiring circuit pattern data;dividing patterns in the circuit pattern data into multiple areas havingdifferent pattern density ranges; and generating dummy pattern data suchthat dummy patterns surround each of the multiple areas to generatedrawing data, wherein the dummy patterns included in the dummy patterndata not printable as a pattern when a resist layer formed on asubstrate is exposed with an electron beam by an electron beamlithography apparatus and is developed, and the dummy pattern data aregenerated such that a variation of pattern density of an entire area issmaller than 10%.
 8. The pattern formation method of claim 7, furthercomprising: dividing the entire area into areas; calculating a patterndensity for each of the areas, wherein the dividing patterns isperformed based on the pattern density of each of the areas.
 9. Thepattern formation method of claim 8, wherein a size of the dummypatterns is less than a resolution limit of a patterning operation usingthe electron beam lithography apparatus.
 10. The pattern formationmethod of claim 8, wherein the dummy pattern data includes periodicallyarranged dummy patterns.
 11. A pattern formation method comprising:acquiring circuit pattern data; calculating a pattern density from thecircuit pattern data; generating dummy pattern data for areas havingpattern density less than a threshold density; generating drawing datafrom the circuit pattern data and the dummy pattern data; drawing, byusing an electron beam from an electron beam lithography apparatus,patterns according to the drawing data on a resist layer formed on asubstrate; and developing the drawn resist layer using a developingsolution, wherein dummy patterns included in the dummy pattern data arenot printed as a pattern when the resist layer is exposed with theelectron beam and is developed.
 12. The pattern formation method ofclaim 11, wherein a dose amount of the electron beam for the dummypatterns included in the dummy patterns data is smaller than a doseamount of the electron beam for circuit patterns included in the circuitpatterns data.
 13. The pattern formation method of claim 12, wherein:the dose amount of the electron beam for patterns corresponding to thedummy patterns data is set smaller than a threshold dose amount, and thethreshold dose amount is less than a dose amount by which the resistlayer forms a pattern by the developing using the developing solution.14. The pattern formation method of claim 11, wherein a size of thedummy patterns is less than a resolution limit of a patterning operationusing the electron beam lithography apparatus.
 15. The pattern formationmethod of claim 11, wherein the dummy pattern data includes periodicallyarranged dummy patterns.
 16. The pattern formation method of claim 11,wherein the dummy pattern data is generated such that a pattern densityof the areas after the dummy patterns is provided is in a range from 0.8times the threshold density to 1.2 times the threshold density.
 17. Thepattern formation method of claim 16, wherein the threshold density isin a range from 20% to 40%.
 18. The pattern formation method of claim11, wherein the dummy pattern data is generated such that the dummypatterns are arranged to surround a dense area having a pattern densityequal to or greater than the threshold density, within a predetermineddistance from the dense area.
 19. The pattern formation method of claim18, wherein the predetermined distance is in a range from 100 μm to 5000μm.
 20. The pattern formation method of claim 11, wherein: a firstthreshold density and a second threshold density different from thefirst threshold density are set as threshold densities, the dummypattern data is generated such that first dummy patterns are arranged tosurround a first area having a pattern density equal to or greater thanthe first threshold density, and second dummy patterns are arranged tosurround a second area having a pattern density equal to or greater thanthe second threshold density, and a pattern density of first dummypatterns is different from a pattern density of second dummy patterns.